Thermodilution is the most frequently used standard method of measuring cardiac output in ICU patients and has come to be considered the Gold standard. This procedure, however has risks associated with it because it requires placement of a pulmonary artery catheter. A new non-invasive method for measuring cardiac output has been developed which using bioimpedence (resistance) in the body for its calculations. This methods utilizes a monitor attached to two electrode pads placed on the patients skin and is therefore much less invasive. The present study is testing the reliability of the cardiac output measurements obtained from this new procedure by comparing results obtained in patients who also are having thermodilution measurements made as well. The GCRC staff will perform the bioimpedance measurements.